1. Field of the Invention
The present invention relates to masks used in X-ray lithography, and more particularly to a technique for making a high resolution X-ray mask with high aspect ratio absorber patterns.
2. Description of the Prior Art
U.S. Pat. No. 4,035,522 issued Jul. 12, 1977 to Hatzakis and entitled X-RAY LITHOGRAPHY MASK describes an X-ray mask for variable resist exposure for use with X-ray lithography so that multilevel devices, using a single exposure of X-rays, can be made.
U.S. Pat. No. 4,328,298 issued May 4, 1982 to Nester entitled PROCESS FOR MANUFACTURING LITHOGRAPHY MASKS discloses a method for manufacturing X-ray lithography masks containing features smaller than 1 micron in size and having conductive or nonconductive substrates. The method involves the initial deposition, as by evaporation, of a very thin coating of a strong X-ray absorber such as gold. A layer of photoresist is applied to the initial gold layer and exposed and developed to remove the photoresist in the exposed areas. Thereafter, the mask is submerged in an electroless gold plating bath. Metals suitable for electroless plating are autocatalytic in nature. Thereafter, additional gold from the bath is preferentially deposited on the exposed first gold layer and is permitted to build to the desired thickness.
U.S. Pat. No. 4,329,410 issued May 11, 1982 to Buckley entitled PRODUCTION OF X-RAY LITHOGRAPHIC MASKS describes a method of depositing X-ray absorber patterns on a mask membrane to achieve minimum pattern feature dimensions less than 1 .mu.m. The membrane is covered with an ultraviolet (UV) sensitive photoresist which carries a thin metallic film. The metallic film is coated with an electron beam resist. The electron beam resist is exposed to the desired pattern by an electron beam. After development, the metal film is etched through the remaining electron beam resist. This forms a stencil overlying the lower UV photoresist layer which is then exposed by an ultra- violet or soft X-ray source. After development, an X-ray absorber, such as gold, is deposited on the membrane. The final exposure step may be done by means of a point source of radiation. The X-ray absorbers will then have sloping walls to prevent shadowing of the X-ray source.
U.S. Pat. No. 4,702,995 issued Oct. 27, 1987 to Okada entitled METHOD OF X-RAY LITHOGRAPHY teaches a method of lithography employing an electromagnetic wave having a very short wave length such as X-ray and a resist layer sensitive to that electromagnetic wave is disclosed. The irradiation process is divided into two steps. One step is selectively irradiating the electromagnetic wave to the resist layer in a desired pattern. The other step is nonselective irradiation over the entire area of the resist layer. The latter step may be conducted with a plurality of workpieces such as semiconductor wafers simultaneously.
U.S. Pat. No. 4,873,162 issued Oct. 10, 1989 to Yoshiska et al entitled X-RAY MASK AND A MANUFACTURE METHOD THEREFOR describes an X-ray mask for X-ray lithography that has an X-ray absorber pattern which is formed from a Ti-W alloy, with a Ti content of 0.5-10 weight %. A method for the manufacture of the X-ray mask comprises sequentially forming a first film, a Ti-W alloy film with a Ti content of approximately 0.5-10 weight %, and a third film on a mask substrate and coating the third film with an electron beam-sensitive resist, exposing the resist to an electron beam and then developing the exposed resist to form a resist pattern, using the resist pattern as a mask and selectively etching the third film to form a pattern, and using the pattern as a mask and selectively etching the Ti-W alloy film with a reactive gas to form an absorber pattern. The Ti-W alloy film is preferably formed by sputtering in an atmosphere of argon and nitrogen gas with a nitrogen content of approximately 30-50%, whereby nitrogen is included in the Ti-W alloy film.